Conventionally, as a correction for unnaturally reproduced color raised in a picked-up image due to the difference of color temperature of a light source illuminating a pick-up subject or a subject to be picked up, there is known a correction that depicts parts, which should fundamentally be white, with white correctly (that is, the white balance correction). For example, a reproduced image which is picked up by an image pick-up device such as a digital still camera using an image pick-up element or a CCD, a CMOS, etc., comes to be a red-tinged image in case the light source is an incandescent lamp, while comes to be a blue-tinged image in case the light source is a fluorescent lamp. So as to correct the unnaturally reproduced color of a picked-up image to natural color, the white balance correction according to color temperature of a light source is performed.
As a method for carrying out the white balance correction, roughly, there are known a method in which color temperature of a light source is measured and the correction is carried out based on thus measured color temperature, and a method in which color information of a picked-up image is analyzed to figure out color temperature of a light source and the correction is carried out. In case of employing the former method, even if comparatively appropriate white balance correction is realized, a structure to measure color temperature of a light source such as a sensor has to be arranged in an image pick-up device, which undesirably enlarge the image pick-up device in size as well as increase the manufacturing cost thereof. Accordingly, various manners to appropriately carry out the white balance correction by employing the latter method have been proposed.
For example, there is known a method in which, assuming that the average of color of an entire picked-up image becomes achromatic color, deviance of the average color balance of color of an entire picked-up image is determined to correct the deviance. In employing this method, the white balance correction can be performed by comparatively easily presuming color temperature of a light source from a picked-up image. However, since this correction manner is based on the assumption that the average of color of an entire picked-up image becomes achromatic color, the white balance correction cannot be correctly carried out as for a picked-up image that does not fulfill the assumption.
United States Patent Application Publication No. US2005/0041115A1 discloses a method that can comparatively appropriately detect white by determining luminance level ranges to which white belongs, and selecting the final white value by performing image division in thus determined luminance level ranges. Specifically, color data of a picked-up image is classified into luminance level ranges of “n” pieces (ranges which are obtained by evenly dividing an interval between the minimum luminance level and the maximum luminance level), and color data which is closest to white is detected based on color data which is classified into “n” luminance levels, and a luminance level to which the color data belongs is selected to the clip luminance level. Next, the picked-up image is divided into regions of “k*m” pieces, and for respective regions, color data that belongs to the clip luminance level range is stored among color data of the regions. Then, in each of the k*m regions, color data closest to white is selected as the white value. Next, among the k*m regions, one region that has the largest number of color data that belongs to the clip luminance level range is selected. Color data that is selected as the white value in the selected region is selected as the final white value. Then, color correction is carried out based on thus selected white value.